Granziera Junior, Francisco, et al. “The Attitude Determination Problem from Two Reference Vectors- a Description of the Triad Algorithm and Its Attitude Covariance Matrix”. Semina: Ciências Exatas E Tecnológicas, vol. 28, no. 1, July 2007, pp. 21-36, doi:10.5433/1679-0375.2007v28n1p21.